The goal of this study is the clarification of the role of membrane-bound iron-sulfur centers in the basic bioenergetic processes of energy-transducing systems. The role of membrane-bound iron-sulfur centers in electron-transfer and energy-conservation reactions will be investigated. The basic analytical technique will be electron paramagnetic resonance (EPR) spectroscopy. One iron-sulfur protein (the Rieske center) has been found in association with the b and c-type cytochromes in mitochondria and its presence will be sought in situ in other energy-transducing systems. A complex analogous to mitochondrial Complex III will be isolated from other membrane systems and the components essential for ATP synthesis will be defined. The possible role of the Rieske iron-sulfur protein as a protein carrier during energy conservation will be tested according to the chemiosmotic hypothesis. The relationship of multiple, bound iron-sulfur centers to known enzymatic functions and to electron-transfer pathways of chloroplasts and chromatophores will be considered. After isolation and characterization, these bound proteins will also be used in experiments to reconstitute the electron-transfer and energy-conservation processes.